When Should I Use `shell=True` with the `subprocess` Module?

Specific Use of 'shell=True' in Subprocess

When utilizing the subprocess module, the 'shell=True' argument serves a specific purpose. While both the following code snippets execute the same process, they differ in their approach:

callProcess = subprocess.Popen(['ls', '-l'], shell=True)
callProcess = subprocess.Popen(['ls', '-l']) # without shell

When to Use 'shell=True'

Invoking 'shell=True' implies that the command will be executed through a shell interpreter, allowing for the expansion of environment variables and file globs. However, this approach carries potential risks:

• Invocation of an Unknown Program: The SHELL environment variable dictates which binary is invoked as the shell, introducing platform-specific behavior.

Preferred Approach

Generally, it is advisable to avoid using 'shell=True'. Here are some reasons:

• Security Vulnerabilities: ILS (input line splitting) attacks can exploit shell-based invocations by manipulating environment variables.
• Platform Dependency: The behavior of the shell varies across platforms, making it difficult to ensure consistent results.

Summary

Unless you have a specific need for shell expansion, it is recommended to set 'shell=False' for subprocess invocations. This ensures that the process is executed directly without relying on an interpreter or introducing unnecessary risks.

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